This invention relates to a magnetic recording medium, and particularly to a protective layer for a magnetic recording medium of the vapor deposition type.
A magnetic recording medium of the vapor deposition type is manufactured by physical and chemical vapor deposition, such as vacuum deposition, sputtering, or ion plating, wherein a ferromagnetic metal is heated in vacuum or a gaseous atmosphere until it vaporizes and deposits physically on a support. Such magnetic recording medium constantly contacts and slides on the transport system and magnetic head in a recording/reproduction apparatus, and it must have high wear resistance, abrasion resistance and lubricity, but none of the conventional products known to date meets these requirements perfectly.
Several methods are known for providing a protective layer for improving the wear resistance of the magnetic recording medium, for example, the technique of electroplating a rhodium film, nickel film, nickel-phosphorus film or nickel-tin film, the technique of oxidizing the surface of a thin cobalt-containing ferromagnetic metal film by exposing it to a suitable temperature and moisture (Japanese Patent Publication No. 20025/67 and U.S. Pat. No. 3,353,166), the technique of contacting a thin magnetic alloy film with nitric acid, treating the same with heat to form an oxide film on the surface, and impregnating the film with a lubricant (British Pat. No. 1,265,175), and the technique of depositing the vapor of chromium on the surface of a thin ferromagnetic metal film in a suitable degree of vacuum to thereby form a layer composed of a mixture of chromium and chromium oxide (Japanese Patent Publication No. 4393/70).
Methods are also known to form a protective layer by vapor deposition, sputtering, or ion plating SiO (U.S. Pat. Nos. 3,109,746, 3,353,166, and Japanese Patent Application (OPI) No. 80102/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), SiO.sub.2 (Japanese Patent Application (OPI) Nos. 93404/75 and 112307/76), noble metals (Japanese Patent Application (OPI) Nos. 93604/75 and 58304/76), and metal oxides, carbides, nitrides, sulfides and fluorides (Japanese Patent Application (OPI) Nos. 104602/75, 123408/75, 146303/75, 56202/76, 21901/78, 21902/78 and 30304/78), but none of the resulting protective layers are completely satisfactory.